Electronic filters detect data, in part, by permitting data signals of predetermined frequencies or data rates to pass through the filter. Various active or passive elements having assigned electrical values are configured, sometimes in cascading sequence, in the filter to optimize the filter's data-detection ability. This optimization necessitates, however, that the filter be "tuned" to the predetermined frequencies or data rates.
Tuning is accomplished by precisely adjusting the relative balance of various inductive and capacitive values assigned to the filter elements. This fine-tuning of the various values can be difficult, especially when filtering data that are transmitted at very high frequencies, e.g., over 1,000 megabits/second.
Thus, to optimize filter data detection at such high data rates, the peak transient response of the data signal needs to be maximized, and its noise bandwidth needs to be minimized. Filter data-detection is improved by causing the filter to generate a voltage ramp output (i.e., a triangular pulse) in response to a digital signal input (i.e., a square pulse). In this way, the filter approximates a perfect matched filter, functioning as an integration over the input pulse period.
These improved filters, however, are not easily tunable due to the necessary fine-tuning of various values assigned to filter elements. Moreover, these improved filters do not readily permit optimum data detection at very high frequencies. Known improved approaches that employ switched-capacitor filters, for instance, are limited operationally only up to a few hundred kilohertz, due at least partly to inherent feedback in those filters.
U.S. Pat. No. 3,559,081 discusses an automatic gain-correcting filter, which is not frequency selective by tuning reactive elements.
U.S. Pat. No. 3.978,416 describes a frequency-tracking filter, which locks over a narrow noise bandwidth onto a noisy signal that is time-varying in the frequency domain.
U.S. Pat. No. 4,383,230 discloses a voltage-tuned active filter, operable only over 10 to 10,000 Hertz. The filter response is derived from feedback networks that allow the construction of simulated inductors.
U.S. Pat. No. 4,716,388 describes a switched capacitor filter, which employs feedback in the network, thereby being limited operationally only up to a few hundred kilohertz.